Ring laser angular rate sensors, commonly referred to as ring laser gyros, are well known and in widespread use today. For example, ring laser gyros are frequently used in guidance and navigation modules on a variety of vehicles, including airplanes, unmanned rockets, and military tanks. In addition, ring laser gyros are used in down-hole drilling operations, such as for oil, for providing precise locations of a drilling bit.
A typical ring laser gyro includes a laser block having a plurality of interconnected passages formed within the block. The passages are arranged in a closed loop polygon shape, such as a triangle or a rectangle, and reflective surfaces are positioned at the intersection of each passage with another passage. In this manner, an optical closed loop path is created within the laser block. A lasing gas, such as helium-neon for example, is contained within the closed loop path.
A pair of electrodes are mounted to the laser block in fluid communication with lasing gas in the closed loop path. One electrode serves as a cathode, and the other electrode serves as an anode. An electrical potential is created across the cathode and anode through the lasing gas. This electrical potential creates a population inversion in the lasing gas, which in turn generates a laser that traverses the optical closed loop path of the laser block. The ring laser gyro can include a third electrode that serves as a second anode. An electrical potential created across the cathode and the second anode creates a counter-rotating laser traversing the optical closed loop path.
An important feature of a ring laser gyro is the seal between the electrodes and the laser block. The electrodes must be sealed to the block in a gas-tight manner to prevent escape of the lasing gas from within the gyro, to prevent the intrusion of ambient gases into the gyro, and to provide mechanical support for the electrode itself. Conventionally, an indium seal is used to mount the electrodes to the laser block. A thin ring of ductile indium is compressed between the electrode and the laser block. Chemical and physical bonds are formed between the indium and the ring laser gyro components (i.e. the laser block and the electrode) during this compression operation.
Electrode seals, however, are subject to delamination when exposed to thermal and mechanical stresses as well as certain reactive solvents and compounds. Such exposure is common during both the manufacture and operation of the gyro. Thermal and mechanical stresses result from design, testing, handling and end use environments. Exposure to reactive solvents and compounds occurs as part of the manufacturing process, end use environment, and gyro operation. Reactive compounds can also be introduced as a result of material selection. An example of the latter stems from the common use of lithium-aluminum-silicate glass ceramic in the design of ring laser gyros. A number of properties of this glass ceramic make it highly desirable as laser block material, however, the material contains reactive alkali metals, such as lithium, which is known to hasten seal degradation, given appropriate seal surface conditions and concomitant contaminants.
The desired extension of gyro usage to applications having ever greater service life requirements, with increasingly severe environmental exposures, creates the need for an electrode seal more durable than those achievable using the current art. Such an improved electrode seal should provide increased durability in the presence of thermal and mechanical stresses, certain reactive solvents and compounds.